Field of the Invention
The present invention relates to a method for producing a toner for developing electrostatic images (electrostatic latent images) for use in image-forming methods, such as electrophotography and electrostatic printing.
Description of the Related Art
With recent advances in computers and multimedia, there has been a demand for means for outputting high-definition full-color images in various fields, including offices and homes.
For business use involving frequent copy and printing, there is a demand for high endurance without deterioration of image quality even after many copies and prints are output. For use in small offices and homes, there is a demand for small apparatuses from the space-saving, energy-saving, and weight-saving perspectives, as well as a demand for high-quality images. In order to meet these demands, it is necessary to improve toner performance, such as environmental stability, soiling of components, low-temperature fixability, development endurance, and storage stability.
In particular, in the case of full-color images formed of superposed color toners, various color toners must be developed in the same manner, otherwise poor color reproduction and color non-uniformity occur. When a pigment or dye used as a colorant for toner is precipitated on the surface of toner particles, this may affect developability and cause color non-uniformity.
Fixability and color mixture properties are important in full-color images. For example, although binder resins suitable for low-temperature fixing are selected in order to meet the demand for high-speed printing, such binder resins greatly affect developability and endurance of color toners.
There is a demand for means for outputting high-definition full-color images for extended periods in different temperature and humidity environments. In order to meet such demands, it is necessary to reduce variations in the amount of electrical charge of toner and variations in toner surface properties due to different operating environments, such as temperature and humidity. It is also necessary to reduce soiling of components, such as a developing roller, a charging roller, a regulating blade, and a photosensitive drum. Thus, there is a demand for toners that have stable chargeability, cause no soiling of components, and have consistent development endurance even after long-term storage in various environments.
Variations in storage stability or in the amount of electrical charge of toner depending on the temperature and humidity can be caused by a release agent or a resin component of the toner bleeding from the interior to the surface of the toner (hereinafter also referred to simply as bleed) and changing the surface properties of the toner.
Such problems may be solved by a method for covering the surface of toner particles with resin.
Japanese Patent Laid-Open No. 2006-146056 discloses a toner having inorganic fine particles firmly adhered to the surface thereof as a toner having good high-temperature storage stability and printing endurance in a normal temperature and humidity environment or in high temperature and high humidity environments. However, even in the toner having inorganic fine particles firmly adhered to toner particles, a release agent or a resin component may bleed through a space between the inorganic fine particles, and the inorganic fine particles may detach from the surface due to degradation. Thus, the endurance of toner and soiling of components in severe environments should be further improved.
Japanese Patent Laid-Open No. 03-089361 discloses a method for producing a polymerized toner by adding a silane coupling agent to a reaction system in order to produce a toner that has no colorant or polar substance exposed on the surface thereof, has a narrow electrical charge distribution, and has the amount of electrical charge largely independent of humidity. However, in such a method, precipitation and hydrolytic polycondensation of a silane compound on the toner surface are insufficient, and environmental stability and development endurance need to be further improved.
Japanese Patent Laid-Open No. 09-179341 discloses a polymerized toner that contains a silicon compound in the form of a continuous thin film on the surface thereof in order to control the amount of electrical charge of the toner and to form high-quality print images at any temperature and at any humidity. However, the polymerized toner has a polar organic functional group, has insufficient precipitation and hydrolytic polycondensation of the silane compound on the surface thereof, and has a low degree of cross-linkage. Thus, it is necessary to reduce variations in image density due to variations in chargeability in high temperature and high humidity environments and to reduce soiling of components due to degradation.
Japanese Patent Laid-Open No. 2001-75304 discloses a polymerized toner having a covering layer formed by adhesion of agglomerates containing a silicon compound as a toner that has improved flowability, a less likelihood of separation of a fluidizer, improved low-temperature fixability, and improved blocking properties. In this polymerized toner, however, a release agent or a resin component may bleed through a space between the agglomerates containing the silicon compound. Furthermore, the silane compound may be insufficiently precipitated on the toner surface or may cause insufficient hydrolytic polycondensation. Thus, it is necessary to reduce variations in image density due to variations in chargeability in high temperature and high humidity environments, to reduce soiling of components due to toner melt adhesion, and to improve storage stability.